Method for the removal of sulphur from molten ferrous metal



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Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE IWETHOD FOR THE REMOVAL OF SULPHUR FROM MOLTE-N FERROUS METAL Charles W. Andrews, Chicago, Ill., assignor to H. A. Brassert & Company, Chicago, Ill., a corporation of Illinois No Drawing. Application February 11, 1938, Serial No. 190.141

2 Claims. (01. 75-55) there are disclosed certain mixtures of limestone,

fluorspar and soda ash which at the time of the application for that patent had been found desirable for use in the reduction of the sulphur content of molten metal.

Since that time work has been continued and a number of important developments have been made bearing on the same subject. Among these is the fact that it has been found fluorspar has as much injurious effect on the ladle lining as soda ash. Another development was that it was found that if the limestone was deposited in the hot ladle too long before the pouring of the molten iron, the results were not as satisfactory. A further development was that by a considerable change in the mixture, sulphurs running about .10% in the molten metal were easily reduced to under .04%, and with good eiiiciency.

It is an object of the present invention to provide a newand improved method and uses of materials for the reduction of the sulphur content in ferrous metals.

It is a further object to provide a method of this character which is economical in the quantity of desulphurizing materials required and which is adapted for efiective commercial use.

Other and further objects will appear as the description proceeds. The continued development work has resulted in finding that a mixture of approximately 31 soda ash, il fluorspar and 60% limestone, results in a sulphur reduction of about from. ch metal and a removal of about 16 lbs. of sulphur per 100 lbs of soda ash, both of which results are very satisfactory as to cost. Contrary to. general expectations, it has been found that approximately 2 lbs. of fluorspar per ton of metal is sufficient to give satisfactory fluidity to the slag so that 'itcan be skimmed off without difficulty.

This new and improved method of operation consists in first placing the soda ash and fluorspar, preferably together, in a ladle heated by a previous charge a sufiicient length of time before the iron is to be tapped from the furnace to thoroughly dry out both the ingredients, thereafter adding the limestone, preferably up to inch in size. The limestone is preferably added only a suflicient time before the molten iron is poured into the ladle to dry out the limestone, but not to cause any material decomposition owing to the heat of the ladle, which normally would be from 900'to 1300 F. If there are ex;- tended delays between repeated fillings of the ladle it is desirable to provide a cover for the ladle to retain its heat. It will readily be seen that this new method of operation comprises an additional step to that disclosed in the above mentioned patent.

As a specific example, on five consecutive days of operation a blast furnace making from 470 to 516 tons of basic iron per day was operated with about 75 to 100 lbs. less limestone per ton of metal than would normally be used. This resulted in the production of iron with an average sulphur content of .103%. Soda ash, .fluorspar and limestone were added as previously outlined, the ratios being 32%, 9 and 58 respectively. The result of this treatment was the reduction of the average sulphur to .038%. Whereas in former practice the fluorspar and soda were ordinarily used in approximately equal quantities, this new practice called for the use of about 2.6 lbs. of fluorspar to 9 lbs. of soda,

'the maximum variation for most effective operation being from 7.39 lbs. to 10.18 lbs. of soda per ton of iron, the fluorspar remaining practically constant at 2.60 to 2.7 7 lbs. It was observed during this run that the reduction in the limestone enabled the production of iron to be increased approximately 50 tons per day, while the cost of the desulphurizing materials wasless than 25 per ton of metal treated, thus showing a substantial savings in operating cost due to the desulphurizingoperation. The amount of the desulphurizing compound required for most efficient and economical operation was found to be from 1.25% to 2% of the weight of the molten iron treated.

Other test runs have also been made and in another specific example the materials were mixed on an average basis for a three day run with 27.79% soda, 10.31% fluorspar and 61.90% limestone. The sulphur content of the iron treated ran as high as .110% with an average of approximately .07. In all cases the sulphur was reduced below .05% and in a" substantial proportion of cases to .035 or below.

A third test run of three days was made with the materials mixed in the proportion of 36.06% soda, 8.98% fluorspar and 54.96% limestone. The sulphur in the iron treated ran higher than in previous tests, in some cases being as high as 190%. A very substantial sulphur reduction resulted from the treatment. In the majority of cases it was reduced to .05% or below and in a number of tests was reduced to below .03%.

V I have found that either calcitic of dclomitic limestone may be used although commercial operation shows that dolomitic limestone is somewhat more effective. While calcium fluoride was used in some cases, it was found that commercial fluorspar was satisfactory and they are to be understood to be equivalents in the present process.

While I have disclosed certain preferred methods of operation and preferred proportions of materials, it is to be understood that they may be varied to meet differing conditions and requirements within the limitations of the appended claims. I claim: 1. A method of purifying molten iron containingsulphur and other inclusions which consists in first placing in a heated ladle, a mixture of about one-fourth to one-sixth fluorspar and the balance soda, allowing the mixture to be heated .by the heat of the ladle, thereafter adding a weight of limestone greater than that of the mix ture, and pouring the molten iron into the ladle before material decomposition of the-limestone takes place.

thereafter adding a weight of limestone greater than that of the mixture, and pouring the molten iron into the ladle before material decomposition of the limestone takes place, t :e total amount of desulphurizing mixture being approximately 1 to 2 percent of the weight of the iron to be treated.

CHARLES W. ANDREWS. 

